There has never been any issue about pricing for the provision of an electric hook-up facilty because the price/cost includes the fixed cost of installation as well as the variable cost of the electricity itself.
What has been illegal, since Ofgem's ruling a few years ago, is to charge more for the supply of the electricity than it's cost.
This ruling was intended, successfully, to stop static site owners charging more for metered electricity than it cost them.
It was never intended to price-cap the provision of the pitch hook-up facility on touring sites which were unmetered, ie virtually all touring sites.
When the ruling came in the bigger touring site operators, including the Caravan Club, had to eliminate the 5% VAT which had been deducted as "electricity energy" rather than the (then) 17.5% applied to standard charges - as this meant sites paying more VAT to HM Revenue, many incorporated the hook-up charge in the pitch fee, with an increase, and used the Ofgem ruling as justification for the increase.
A site operator can make any FIXED charge they want for an unmetered hook-up facility - as long as all their charges are clear at time of booking there can be no complaint. If you don't like the total cost, don't make the booking. it's not a rip-off, it's supply and demand, if you don't pay it others will.